Surface-roughened resin film, metal sheet coated with surface-roughened resin film, process for producing metal sheet coated with surface-roughened resin film, and metal can having surface coated with surface-roughened resin film and process for producing the same

ABSTRACT

It is intended to provide a metal can from which the contents packed therein are easy to take out and which has been coated with a polyester resin film for food or with a film for food which is made of a resin consisting mainly of a polyester resin; a metal sheet which has been coated with a surface-roughened resin film and is for use in the metal can; a surface-roughened resin film for use in the metal sheet; and processes for producing these. The surface-roughened resin film is one which comprises a polyester resin and, incorporated therein, either inorganic particles or a resin incompatible with the polyester resin, e.g., a polyolefin resin, to thereby have a roughened surface. Alternatively, the surface-roughened resin film is one obtained by embossing a surface of a resin film. The surface-roughened resin film is laminated to a metal sheet. Alternatively, a resin film which has not undergone surface roughening is laminated to a metal sheet and this resin film-coated metal sheet is embossed. The resultant resin film-coated metal sheet is formed into a can by drawing or by drawing with ironing. The surface roughness is thus enhanced.

TECHNICAL FIELD

The present invention relates to a surface-roughened resin film, a metalsheet coated with a surface-roughened resin film, a process forproducing the metal sheet coated with a surface-roughened resin film,and a metal can having a surface coated with a surface-roughened resinfilm and a process for producing the metal can.

BACKGROUND ART

In recent years, a metal can for food formed by processing a metal sheetcoated with a resin film, particularly a polyester resin has been widelyplaced on the market. Such a can obtained by using a metal sheet coatedwith a polyester resin has an extremely smooth surface. However, due tothis smoothness, when the contents packed in the can are taken out, theyfirmly adhere to the surface of the can, therefore, there is a drawbackthat it is difficult to take out.

In order to overcome the drawback, the present invention makes it anobject to provide a metal can from which the contents packed therein areeasy to take out and which has been coated with a polyester resin filmfor food or with a film for food which is made of a resin consistingmainly of a polyester resin; a metal sheet which has been coated with asurface-roughened resin film and is for use in the metal can; asurface-roughened resin film for use in the metal sheet; and processesfor producing these.

DISCLOSURE OF THE INVENTION

In order to solve the foregoing problem, the present invention makes itan ultimate object to obtain a metal can for food, in which the surfaceof a polyester resin film coated on a metal sheet, which becomes theinner surface of the can, has been roughened.

In other words, a surface-roughened polyester resin film of the presentinvention is a surface-roughened resin film characterized in that itcomprises a polyester resin film whose surface roughness Ra (JIS B 0601)is 0.2 μm or greater, preferably Ra (JIS B 0601) is 0.5 μm or greater;in addition,

-   -   it has been formed by extruding a polyester resin obtained by        incorporating therein 1% or more by weight of an inorganic        particle with a particle size of 1 μm or greater; and further,    -   the inorganic particle is one or more kinds of titanium dioxide,        zinc oxide, calcium carbonate and silicone dioxide.

In addition, the surface-roughened resin film of the present inventionis characterized in that it has been formed by extruding a resinobtained by incorporating in the polyester resin 5 to 30% by weight of aresin incompatible with the polyester resin; and further

-   -   the resin incompatible with the polyester resin is one or more        kinds of a polyolefin resin and polymethylmethacrylate.

Further, the surface-roughened resin film of the present invention maybe a surface-roughened resin film comprising a two-layer film consistingof any of the foregoing surface-roughened resin films as the upper layerfilm and a lower layer film which has been provided thereunder and iscomposed of a resin obtained by blending one or more kinds of polyesterresins and a polyolefin component composed of at least one kind selectedfrom the group consisting of a polyolefin resin and polyolefinelastomer. In this case,

-   -   the surface-roughened resin film of the present invention is a        surface-roughened resin film according to claim 6 characterized        in that:    -   a polyolefin resin or a resin composed of a polyolefin resin and        polyolefin elastomer is used as the polyolefin component; in        addition,    -   the polyolefin resin is a resin composed of one or more kinds of        polymer resins of 1-alkene having 2 to 8 carbon atoms; further,    -   the 1-alkene polymer resin is any of polyethylene,        polypropylene, ethylene-propylene copolymer; further,    -   the polyolefin resin is a polyolefin resin obtained by        polymerization with a metallocene catalyst; further    -   at least a part of the polyolefin resin is a modified polyolefin        resin obtained by modification with any of maleic anhydride,        acrylic acid, acrylic ester and diglycidyl methacrylate; in        addition,    -   the polyolefin elastomer is ethylene-propylene copolymer        elastomer produced in plant with a melt flow rate (MFR: 230° C.)        of 0.4 to 30 g/10 minutes; and    -   the blended resin constituting the lower layer film contains 1        to 30% by weight of the polyolefin component.

A metal sheet coated with a surface-roughened resin film of the presentinvention is characterized in that it is a metal sheet coated with asurface-roughened resin film formed by laminating any of the foregoingsurface-roughened resin films to a metal sheet; or

-   -   it is a metal sheet coated with a surface-roughened resin film        formed by being coated with a polyester resin film having an        uneven pattern formed on the surface by an embossing process;        and    -   the surface roughness Ra (JIS B 0601) of the surface-roughened        resin film is 0.2 μm or greater, preferably Ra (JIS B 0601) is        0.5 μm or greater.

A process for producing a metal sheet coated with a surface-roughenedpolyester resin film of the present invention is a production methodcharacterized by laminating any of the foregoing surface-roughened resinfilms through an adhesive or directly to a metal sheet without anadhesive; or

-   -   by laminating a polyester resin film having an uneven pattern        formed on the surface by an embossing process through an        adhesive or directly to a metal sheet without an adhesive; or    -   by laminating a polyester resin film through an adhesive or        directly to a metal sheet without an adhesive and then embossing        the surface of the polyester resin film.

A metal can of the present invention is a metal can formed by processinga metal sheet coated with a resin film, characterized in that it is ametal can having a surface coated with a surface-roughened resin film inwhich the surface roughness Ra (JIS B 0601) of the resin film afterbeing formed into a can is 0.5 μm or greater, and that the resin film isa polyester resin film.

Alternatively, the metal can of the present invention is a metal canformed by processing any of the foregoing metal sheets coated with asurface-roughened resin film; or

-   -   a metal can formed by processing a metal sheet coated with a        resin film by drawing or by drawing with ironing with the use of        a punch whose surface has been roughened so as to have the        foregoing surface coated with a surface-roughened resin film.

A process for producing a metal can of the present invention is aprocess for producing a metal can having a surface coated with asurface-roughened resin film characterized by processing a metal sheetcoated with a polyester resin film and forming it into a can body bydrawing or by drawing with ironing with the use of a punch whose surfacehas been roughened.

BEST MODE FOR CARRYING OUT THE INVENTION

The inventors of the present invention intensively studied in order toovercome the foregoing drawback, and as a result, they found out that byroughening the surface of a resin film that becomes the inner surface ofa can formed by extruding a metal sheet coated with a resin film, thecontents packed in the can can be easy to take out without firmlyadhering to the can wall. Hereunder, the present invention will beexplained in detail.

The metal can for food of interest of the present invention is composedof a resin-coated film metal sheet obtained by laminating to a metalsheet a resin film whose surface has been roughened, in particular asingle-layer resin film whose surface has been roughened byincorporating an inorganic particle or a resin incompatible with apolyester resin in the polyester resin, or a two-layer film consistingof, the same single-layer resin film as above as the upper layer and aresin film composed of a resin obtained by blending a polyester resinand a polyolefin component as the lower layer, and roughening thesurface of the upper layer film.

With regard to the metal can coated with a surface-roughened resin filmof the present invention, it is preferred that the resin film which willbe the innermost surface of the can has been roughened after beingformed into a can by drawing or by drawing with ironing, in particular,has a surface roughness Ra of 0.5 μm or greater. If the surfaceroughness Ra is less than 0.5 μm, it will be difficult to take out thecontents packed in the can.

In order that the surface of the resin film after being formed into acan has been roughened, as mentioned below:

-   1) a process for processing a metal sheet coated with a resin film    and forming it into a can by drawing or by drawing with ironing with    the use of a punch whose surface has been roughened;-   2) a process for laminating a resin film to a metal sheet,    undergoing an embossing process to form an uneven pattern on the    surface of the resin film, processing the metal sheet coated with a    surface-roughened resin film and forming it into a can;-   3) a process for forming a can by processing a metal sheet coated    with a surface-roughened resin film, which has been obtained by    undergoing an embossing process to form an uneven pattern on the    surface of the resin film and laminating the resin film to a metal    sheet;-   or the like is employed, however, without undergoing an embossing    process, a resin film whose surface has been roughened in advance is    laminated to a metal sheet to form a metal sheet coated with a    surface-roughened resin film, then this metal sheet coated with a    surface-roughened resin film may be processed and formed into a can.

With regard to the surface-roughened resin film and the metal sheetcoated with a surface-roughened resin film of the present invention, itis preferred that the surface of the resin film has in particular asurface roughness Ra of 0.2 μm or greater in the sate of film or in thestate of being laminated to a metal sheet. If the surface roughness Rais less than 0.2 μm, it will be difficult to obtain the surfaceroughness Ra of 0.5 μm or greater after being formed into a can.

The resin film whose surface has been roughened in advance withoutundergoing an embossing process, which is the surface-roughened resinfilm of the present invention, can be obtained as follows.

1) By extruding a polyester resin obtained by incorporating therein 1%or more by weight of one or more kinds of inorganic particles such astitanium dioxide, zinc oxide, calcium carbonate and silicone dioxidehaving a particle size of 1 μm or greater, a surface-roughened polyesterresin film is formed. With regard to the formed film, the inorganicparticles project from the surface, whereby the surface is roughened. Inthis case, if the content of the inorganic particles with a particlesize of 1 μm or greater is less than 1% by weight, the surface roughnessRa of 0.2 μm or greater cannot be obtained after being formed into afilm.

2) By extruding a resin obtained by incorporating in a polyester resin 5to 30% by weight of one or more kinds of resins incompatible with thepolyester resin selected from a polyolefin resin such as polyethylene,polypropylene and ethylene-propylene copolymer, andpolymethylmethacrylate, a surface-roughened polyester resin film isformed. Since these resins are incompatible with a polyester resin, whena film is formed by extruding both resins after heating and melting,these resins incompatible with the polyester resin are present in aparticulate form in a state of being dispersed in the polyester resin,and the incompatible resin particles project from the film surface,whereby the surface is roughened.

In this case, if the content of the polyolefin resin,polymethylmethacrylate or the like to be incorporated in the polyesterresin is less than 5% by weight, the surface roughness Ra of 0.2 μm orgreater cannot be obtained after being formed into a film. On the otherhand, if the content exceeds 30% by weight, the dispersed state willbecome ununiform, whereby it will be significantly difficult to obtain adesired state of the roughened surface.

The foregoing resin film composed of a resin obtained by incorporatingin a polyester resin a resin incompatible with the polyester resin has asomewhat poor adhesiveness to a metal sheet, whereby, it may be detachedwhen being formed into a can by drawing or by drawing with ironing insome cases. Therefore, a layer excellent in adhesiveness to both of theresin film and the metal sheet may be interposed therebetween. In otherwords, by producing a two-layer film consisting of a resin film composedof a resin obtained by incorporating a resin incompatible with thepolyester resin in the polyester resin as the upper layer film, and alower layer film which has been provided thereunder and is composed of aresin obtained by blending a polyester resin and a polyolefin componentselected from the group consisting of a polyolefin resin and polyolefinelastomer, by using the coextrusion method, and by laminating it to ametal sheet so as to bring the lower layer film into contact with themetal sheet, whereby a favorable adhesiveness to the metal sheet can beobtained.

Examples of the incompatible polyolefin resin to be incorporated in thepolyester resin in the single layer film or in the upper layer of thetwo-layer film, and the polyolefin resin to be used as the polyolefincomponent to be blended with a polyester resin in the lower layer of thetwo-layer film may include a resin composed of one or more kinds ofcopolymer resins of 1-alkene having 2 to 8 carbon atoms. Examples of thecopolymer resin of 1-alkene having 2 to 8 carbon atoms may include lowdensity polyethylene, medium density polyethylene, high densitypolyethylene, polypropylene, polybutene-1, polypentene-1, polyhexene-1,polyheptene-1, polyoctene-1, ethylene-propylene copolymer,ethylene-butene-1 copolymer, ethylene-hexene copolymer and the like.

Among these, as the polyolefin component to be blended with thepolyester resin in the lower layer of the two-layer film,ethylene-propylene copolymer particularly produced in plant ispreferred. Further, in the case of using the polyolefin resin obtainedwith a metallocene catalyst as the polyolefin resin, an oligomer thataffects the flavor of the contents packed in the can is generated in asmall amount, therefore it is preferred.

In addition, a modified polyolefin resin obtained by modifying thepolyolefin resin to be blended with the polyester resin in the lowerlayer of the two-layer film (such as polyethylene or polypropylene) withany of maleic anhydride, acrylic acid, acrylic ester, acrylate ionomerand diglycidyl methacrylate can be used. By using the one in which sucha modified polyolefin resin has been blended at a ratio of 1 to 100% byweight relative to the unmodified polyolefin resin as the polyolefincomponent, the polyolefin component is dispersed finely in the polyesterresin, and moreover, the adhesiveness to the metal sheet is improved,therefore, it is preferred.

As the polyolefin elastomer to be blended with the polyester resin inthe lower layer of the two-layer film, it is preferred to useethylene-propylene copolymer elastomer with a melt flow rate (MFR: 230°C.) of 0.4 to 30 g/10 minutes, particularly 8 to 25 g/10 minutes. In thecase where the MFR is lower than the foregoing range, the melt viscositywhen heating and melting the resin becomes much higher than that of thepolyester resin, and the particle size of the polyolefin resin to bedispersed in the polyester resin becomes large, therefore it will bedifficult to obtain a favorable state of roughened surface and theimpact resistance will be poor. Accordingly, after coating the metalsheet therewith or forming the coated metal sheet into a can, an impactsuch as dropping or hitting the cans each other is brought about, theresin film is cracked, the crack reached the upper layer film, and thecontents are directly contacted with the metal sheet, whereby the metalsheet is corroded and perforated in some cases. On the other hand, ifthe MFR exceeds the foregoing range, the impact resistance will be alsopoor. This ethylene-propylene copolymer elastomer is preferably the oneproduced in plant.

It is preferred that the blending ratio of the polyolefin component tobe blended with the polyester resin in the lower layer of the two-layerfilm is 1 to 30% by weight relative to the polyester resin. If it isless than 1% by weight, the impact resistance will be poor after coatingthe metal sheet therewith or forming the coated metal sheet into a can.On the other hand, if the blending ratio exceeds 30% by weight, it willbe difficult to obtain a uniform film, and the hardness will bedecreased, whereby the surface of the resin will become likely to bescratched.

Examples of the polyester resin to be used in the single-layer film orin the upper layer of the two-layer film include a homopolymer obtainedby polycondensation of one kind selected from dicarboxylic acids such asterephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalene dicarboxylic acid, diphenylcarboxylic acid, diphenoxyethane dicarboxylic acid, diphenylsulfonecarboxylic acid, anthracene dicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexane dicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalicacid, malonic acid, dimethylmalonic acid, succinic acid,3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid,adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid,azelaic acid, dimer acid, sebacic acid, suberic acid and dodecadicarboxylic acid, and diols such as ethylene glycol, propylene glycol,hexamethylene glycol, neopentyl glycol, 1,2-cyclohexane dimethanol,1,4-cyclohexane dimethanol, decamethylene glycol, 1,3-propanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol,2,2-bis(4′-hydroxyphenyl)-propane and bis(4-hydroxyphenyl)sulfone, acopolymer obtained by polycondensation of one or more kinds ofdicarboxylic acids with two or more kinds of diols, a copolymer obtainedby polycondensation of two or more kinds of dicarboxylic acids with oneor more kinds of diols, and a blended resin obtained by blending two ormore kinds of these homopolymers and copolymers, and any polyester resincan be used, however, a copolymer of ethylene terephthalate and ethyleneisophthalate or polybutylene terephthalate is preferably used. Inparticular, a polyester resin composed of 85 to 95 mol % of ethyleneterephthalate and 5 to 15 mol % of ethylene isophthalate is excellent inprocessability. As described above, even if after the polyester resin inwhich an inorganic particle or a resin incompatible with the polyesterresin has been incorporated is laminated to a metal sheet, it isprocessed and formed into a can by drawing or by drawing with ironing, acrack is not generated in the resin film, and it is excellent inadhesiveness to metal sheet. Further, even if it is contacted with thecontents packed in the can, it does not impair the flavor or the tasteof the contents, and it shows a favorable flavor property.

In addition, polybutylene terephthalate is easy to blend with apolyolefin resin or another polyolefin component, polyolefin elastomer.For example, in the case where it is blended with a polyolefin resin,the polyolefin resin will be dispersed finely in the blended resin,whereby it is effective in forming an appropriate roughened surface andimproving the impact resistance and processability. Further,polybutylene terephthalate has a high crystallization rate, therefore,it has a property of inhibiting the growth of a fragile and coarsecrystal when a metal sheet coated with a resin is processed and formedinto a can, and then the can is heated for painting the outer surface.Therefore, it is extremely effective in improving the impact resistance.In addition, a resin obtained by incorporating a polyolefin resin orpolymethylmethacrylate in polybutylene terephthalate or in a blendedresin of polybutylene terephthalate and another polyester resin isexcellent in resistance to water deterioration (hydrolyzability). Evenif a can formed by processing a metal sheet coated with a film composedof this resin is packed with a water-based content and left for a longtime, reduction of the molecular weight of the resin is small,therefore, a favorable impact resistance can be stably maintained for along time.

In the present invention, the foregoing polyester resin to be used inthe single-layer resin film or in the upper layer resin film of thetwo-layer film obtained by incorporating therein an inorganic particleor a polyolefin resin incompatible with the polyester resin, and theforegoing polyester resin to be blended with a polyolefin component,which is used in the lower layer resin film of the two-layer film makesit possible to carry out a severe process such as drawing or drawingwith ironing without generating a crack, split, scratch, detachment orthe like of the resin film. Therefore, it is premised that the polyesterresin is used in an unoriented state which is excellent in moldingprocessability, thus it is necessary to enhance the intrinsic viscosityto reinforce the resin. Accordingly, the intrinsic viscosity of theforegoing polyester resin is preferably in the range of 0.5 to 1.5, morepreferably in the range of 0.8 to 1.2. In the case where a polyesterresin with an intrinsic viscosity of less than 0.5 is used, the resinstrength is extremely decreased, whereby it becomes difficult to form acan by processing the metal sheet coated with a surface-roughened resinfilm by drawing or by drawing with ironing. In addition, the flavorproperty becomes poor. On the other hand, in the case where theintrinsic viscosity exceeds 1.5, the melt viscosity when heating andmelting the resin becomes extremely high, whereby it becomes extremelydifficult to perform the operation of laminating the melted resin to themetal sheet by extrusion.

In the case where the foregoing surface-roughened resin film is asingle-layer film, it is preferred that it has a thickness of 5 to 50μm. In the case where it is a two-layer film, it is preferred that theupper layer has a thickness of 3 to 15 μm, and the lower layer has athickness of 2 to 47 μm, and further, it has a thickness of 5 to 50 μmin total.

Next, the metal sheet coated with a surface-roughened resin film of thepresent invention will be explained. The metal sheet coated with asurface-roughened resin film of the present invention can be produced asfollows. In other words, a metal sheet is heated to a temperature whichis higher than the melting temperature of the foregoing single-layersurface-roughened resin film by 20 to 40° C., the surface which has notbeen roughened of the surface-roughened resin film is brought intocontact with the heated metal sheet, and they are held by using a pairof laminate rolls and bonded under pressure. Alternatively, a metalsheet is heated to a temperature which is higher than the meltingtemperature of the foregoing lower layer film of the two-layersurface-roughened resin film by 20 to 40° C., the surface of the lowerlayer film of the two-layer surface-roughened resin film is brought intocontact with the heated metal sheet, and they are held by using a pairof laminate rolls and bonded under pressure for lamination. In the casewhere a stronger adhesiveness between the metal sheet and thesurface-roughened resin film is required, they may be laminated byinterposing an adhesive between the metal sheet and thesurface-roughened resin film. In other words, an adhesive such as anurethane-based adhesive or an epoxy-based adhesive is applied on thesurface to be bonded of either the metal sheet or the surface-roughenedresin film in advance, then they are bonded under pressure as describedabove for lamination.

The metal sheet coated with a surface-roughened resin film of thepresent invention can be also produced as follows. In other words, it isproduced by either the method of laminating a resin film to a metalsheet, then performing an embossing process to form a metal sheet coatedwith a surface-roughened resin film having an uneven pattern formed onthe surface of the resin film (the post-processing method), or themethod of laminating a resin film having an uneven pattern formed on thesurface by an embossing process to a metal sheet to form a metal sheetcoated with a surface-roughened resin film (the pre-processing method).

First, the case where the metal sheet is produced by using thepost-processing method will be explained. First, any of the foregoingpolyester resins is heated and melted, and a resin film with a thicknessof 5 to 50 μm is formed by the extrusion method. Then, this resin filmis laminated to a metal sheet. As the method for lamination, any methodsuch as a known heat bonding method, a method of using an adhesive suchas an urethane-based adhesive or an epoxy-based adhesive, or a method ofheat bonding by interposing an adhesive between a metal sheet and aresin film may be employed. Alternatively, a heated and melted polyesterresin may be directly extruded on a metal sheet for lamination. In thiscase, by extruding a polyester resin on a metal sheet on which anadhesive has been applied in advance, they can be laminated byinterposing an adhesive between a metal sheet and a resin film.

The thus obtained metal sheet coated with a resin film is heated so thatthe temperature of the surface of the resin film reaches theglass-transition temperature of the resin film or higher. Then, by usingthe other roll of a pair of rolls consisting of an emboss roll whosesurface has been roughened so as to have a surface roughness Ra of 0.2μm or greater as one roll, and a roll having an elastic body on thesurface as the other roll, the emboss roll is brought into contact withthe resin film, the heated metal sheet coated with the resin film asdescribed above is held and pressure is applied, whereby the pattern ofthe roughened surface of the emboss roll is transferred to the surfaceof the resin film, so that the surface roughness Ra of the resin film ismade 0.2 μmor greater.

Next, the case where the metal sheet is produced by using thepre-processing method will be explained. First, in accordance with theforegoing steps of the post-processing method, any of the foregoingpolyester resins is heated and melted and a resin film is formed. Then,this resin film is heated so that the temperature reaches theglass-transition temperature of the resin film or higher. Then, by usingthe other roll of a pair of rolls consisting of an emboss roll whosesurface has been roughened so as to have a surface roughness Ra of 0.2μm or greater as one roll, and a roll having an elastic body on thesurface as the other roll, a metal sheet coated with the resin filmheated as described above is held and pressure is applied, whereby thepattern of the roughened surface of the emboss roll is transferred tothe surface of the resin film, so that the surface roughness Ra of theresin film is made 0.2 μm or greater.

Then, a metal sheet is heated to a temperature of the melting point ofthe embossed resin film ±10° C., the resin film is brought into contactwith the heated metal sheet, and the embossed resin film and the metalsheet are held and pressure is applied for bonding by using a pair oflaminate rolls. In the case where an excellent adhesiveness between themetal sheet and the resin film is required, it is preferred that anadhesive is interposed between the metal sheet and the resin film andheat bonding is performed as described above.

As described above, the metal sheet coated with a surface-roughenedresin film of the present invention can be obtained.

As the metal sheet, a variety of surface-treated steel sheets such aselectrolytic chromate-treated steel sheet (tin free steel, hereinafterreferred to as TFS) and tin coated steel sheet (tin plate, hereinafterreferred to as tin plate), which are widely used as a common materialfor can, and aluminum alloy sheet can be used. As the surface-treatedsteel sheet, preferred is TFS obtained by forming a two-layer filmconsisting of a lower layer composed of metal chromium in a coatingamount of 10 to 200 mg/m² and an upper layer composed of hydratedchromium oxide in a coating amount of 1 to 30 mg/m² in terms ofchromium, which has a sufficient adhesiveness to the surface-roughenedresin film of the present invention and further has a corrosionresistance. As the tin plate, preferred is the one obtained by coatingthe surface of steel sheet with tin in a coating amount of 0.1 to 11.2g/m², and forming thereon a two-layer film composed of metal chromiumand hydrated chromium oxide in a coating amount of 1 to 30 mg/m² interms of chromium, or the one obtained by forming a single-layer filmcomposed of only hydrated chromium oxide. In either case, the steelsheet to be used as the substrate is preferably a low carbon cold-rolledsteel sheet which is commonly used as material for can. The thickness ofthe steel sheet is preferably 0.1 to 0.32 mm. With regard to thealuminum alloy, preferred is a JIS 3000 series alloy or a JIS 5000series alloy. Further, preferred is the one obtained by undergoing anelectrolytic chromate treatment on the surface thereby forming atwo-layer film consisting of a lower layer composed of metal chromium ina coating amount of 0 to 200 mg/m² and an upper layer composed ofhydrated chromium oxide in a coating amount of 1 to 30 mg/m² in terms ofchromium, or the one obtained by undergoing a chromic phosphatetreatment, whereby a chromium component of 1 to 30 mg/m² in terms ofchromium and a phosphorous component of 0 to 30 mg/m² in terms ofphosphate are adhering. The thickness of the aluminum alloy sheet ispreferably 0.15 to 0.4 mm.

Next, the metal can having a surface coated with a surface-roughenedresin film of the present invention will be explained. The metal canhaving a surface coated with a surface-roughened resin film of thepresent invention can be obtained by processing any of the foregoingmetal sheets coated with a surface-roughened resin film and forming itinto a can. Examples of the can include a three-piece welded canobtained by forming a cut sheet into a cylindrical form by bending orrolling up, forming a can barrel by welding the overlapped edges, andforming a can body by seaming a top plate and a bottom plate to bothupper and lower parts of the can barrel, a two-piece can such as aso-called drawn can obtained by punching out a blank in a form ofcircular plate or the like, forming it into a can barrel by a drawingprocess, and forming a can body by seaming a top plate to the upper partof the can barrel, a so-called thin-walled drawn can obtained bythinning the wall of a can barrel by undergoing a bending and unbendingprocess during the drawing process to form a can barrel and forming acan body by seaming a top plate to the upper part of the can barrel, ora so-called drawn and ironed can obtained by forming a blank into a cupshape by a drawing process, forming a can barrel by thinning the wallpart of the cup by an ironing process, and forming a can body by seaminga top plate to the upper part of the can barrel.

With regard to the inner surface of the three-piece can or two-piece canformed by processing the metal sheet coated with a surface-roughenedresin film of the present invention, the surface roughness Ra of theresin film of the inner surface of the can is preferably 0.5 μm orgreater so that the contents packed in the can are easy to take out. Inthe case of forming it into a three-piece can, the surface of the resinfilm of the metal sheet coated with a surface-roughened resin film ishardly subjected to a processing, therefore the surface roughness of theresin film is hardly changed practically. Accordingly, in the case ofapplying the metal sheet coated with a surface-roughened resin film ofthe present invention to a three-piece can, it is preferred to use ametal sheet coated with a surface-roughened resin film whose surfaceroughness Ra of the resin film is 0.5 μm or greater.

In the case of forming it into a two-piece can by undergoing any of adrawing process, a thinning and drawing process and a drawing andironing process, with regard to the surface of the resin film of themetal sheet coated with a surface-roughened resin film, the surfaceroughness of the resin film is increased by any of these processes. Dueto this, in the case of processing a metal sheet coated with asurface-roughened resin film whose surface roughness Ra of the resinfilm is 0.2 μm or greater and forming it into a two-piece can byundergoing any of these processes, a can whose surface roughness Ra ofthe resin film is 0.5 μm or greater can be obtained after theprocessing.

A can whose surface roughness Ra of the resin film of the inner surfaceof the can is 0.5 μm or greater can be obtained as follows. In otherwords, a metal sheet coated with a resin film is formed by using eitherthe method of heating and melting the foregoing polyester resin anddirectly extruding it on the foregoing metal sheet, or the method offorming a film from the foregoing polyester resin and laminating theresin film to the metal sheet. When processing a blank obtained bypunching it out from this metal sheet coated with a resin film in ashape of circular plate or the like and forming it into a two-piece canby undergoing any of the foregoing drawing process, thinning and drawingprocess and drawing and ironing process, they are processed by using apunch whose surface has been roughened so as to have a surface roughnessRa of 0.5 μm or greater in the final step, and the pattern of theroughened surface of the punch is transferred to the surface of theresin film, whereby the surface roughness Ra of the surface of the resinfilm can be made 0.5 μm or greater.

EXAMPLES

Hereunder, the present invention will be explained in more detail withreference to the Examples.

Example 1 Sample Numbers 1 to 16

A single-layer surface-roughened resin film with a thickness shown inTable 3 was produced by using the extrusion method, which was obtainedby incorporating, in a polyester resin (represented by PES in the table,hereinafter the same as above) consisting of the resin composition shownin Table 1, an inorganic particle whose type and particle size are shownin Table 2 or a resin incompatible with the polyester resin, which wasany of, as shown in Table 3, polyethylene (represented by PE in Table 3,hereinafter the same as above), polypropylene (represented by PP inTable 3, hereinafter the same as above), ethylene-propylene copolymer(represented by EP in Table 3, hereinafter the same as above), andpolymethylmethacrylate (represented by PMC in Table 3, hereinafter thesame as above) at a content (% by weight) shown in Table 3. The surfaceroughness Ra (JIS B 0601) of these single-layer films was measured byusing a surface roughness meter (Surfcom 1500A, manufactured by TokyoSeimitsu Co., LTD). The results are shown in Table 3.

As the polyethylene, polypropylene or ethylene-propylene copolymer, thematerial synthesized with a metallocene catalyst was used in all cases.TABLE 1 Resin composition Resin number Resin composition PES1polyethylene terephthalate (IV value: 0.75) PES2 polyethyleneterephthalate (IV value: 0.82) PES3 polyethylene terephthalate (IVvalue: 1.1) PES4 ethylene terephthalate-ethylene isophthalate copolymer(ethylene isophthalate: 5 mol %)(IV value: 0.9) PES5 ethyleneterephthalate-ethylene isophthalate copolymer (ethylene isophthalate: 10mol %)(IV value: 0.9) PES6 ethylene terephthalate-ethylene isophthalatecopolymer (ethylene isophthalate: 15 mol %)(IV value: 1.5) PES7 ethyleneterephthalate-ethylene adipate copolymer (ethylene adipate: 10 mol %)(IVvalue: 0.6) PES8 ethylene terephthalate-ethylene naphthalate copolymer(ethylene naphthalate: 10 mol %)(IV value: 0.9) PES9 polybutyleneterephthalate (IV value: 1.2)

TABLE 2 Type and particle size of inorganic particle Inorganic materialInorganic particle number Type Particle size (μm) T1 TiO₂ 1.5 Z1 ZnO 2.5C1 CaCO₃ 1.0 S1 SiO₂ 0.5 S2 SiO₂ 1.5 S3 SiO₂ 3.5

Example 2 Sample Numbers 17 to 31

A two-layer surface-roughened resin film with a thickness shown in Table5 was produced by the coextrusion method, which consisted of, as theupper layer film, any one of the resin films of the sample numbers 11,13, 14 and 15 shown in Table 3, composed of a resin obtained byincorporating ethylene-propylene copolymer, which was a resinincompatible with a polyester resin in ethylene terephthalate-ethyleneisophthalate copolymer, which was the polyester resin, and a lower layerfilm which had been provided thereunder and was composed of a resinobtained by blending the polyester resin shown in Table 3 and apolyolefin component selected from the group consisting of a polyolefinresin shown in Table 4 (represented by POL in Table 4, hereinafter thesame as above) and polyolefin elastomer (represented by PEL in Table 4,hereinafter the same as above) at a content (% by weight) shown in Table5. The surface roughness of these two-layer surface-roughened resinfilms was measured in the same manner as in Example 1. The results areshown in Table 5.

As the olefin resin, the material synthesized with a metallocenecatalyst was used in all cases. In addition, as the polyolefinelastomer, the material produced in plant was used. TABLE 3Surface-roughened resin film Inorganic particle Incompatible resin Resinfilm Inorganic Content Content Surface Sample Resin material (% by (% byThickness roughness number type number weight) Type weight) (μm) (Ra:μm) Category 1 PES1 T1 5 — — 20 0.35 Present invention 2 PES2 T1 2 — —20 0.24 Present invention 3 PES3 T1 3 — — 10 0.29 Present invention 4PES4 Z1 2 — — 30 0.38 Present invention 5 PES5 C1 7 — — 50 0.20 Presentinvention 6 PES6 S1 3 — — 20 0.16 Comparative example 7 PES7 S2 3 — — 200.28 Present invention 8 PES8 S3 1 — — 5 0.68 Present invention 9 PES9C1 + S3 2 + 2 — — 30 0.77 Present invention 10 PES2 — — PP 3 25 0.11Comparative example 11 PES2 — — PP 5 25 0.20 Present invention 12 PES5 —— PE 10 25 0.33 Present invention 13 PES9 — — PE 30 25 0.74 Presentinvention 14 PES6 — — EP 20 25 0.47 Present invention 15 PES1 — — PMC 2025 0.44 Present invention 16 PES4 — — PE + PMC 10 + 10 25 0.46 Presentinvention

Example 3 Sample Numbers 32 to 43

The single-layer surface-roughened resin films indicated by the samplenumbers 2, 6, 8, 11, 14 and 15 shown in Table 3 and the two-layersurface-roughened resin films indicated by the sample numbers 18, 20,22, 24, 26 and 31 shown in Table 5 were laminated to any of thefollowing three surface-treated steel sheets shown in Table 6, wherebymetal sheets coated with a surface-roughened resin film were produced.In other words, these metal sheets were heated and the surface oppositeto the roughened surface of these surface-roughened resin films wasbrought into contact with one side of the metal sheet, and the otherside was brought into contact with a white polyester resin film(ethylene terephthalate (88 mol %)-ethylene isophthalate (12 mol %)copolymer, (represented by white ET (88)-EI(12) in Table 6) with athickness of 20 μm containing titanium oxide pigment, and they werelaminated by applying pressure to the three materials by holding themwith a pair of press-bonding rolls. For some of the surface-roughenedresin films, the ones whose surface opposite to the roughened surface,which was to be contacted with a metal sheet, was applied with anepoxy-based adhesive were used, and they were laminated so that theadhesive was interposed between the surface-roughened resin film and themetal sheet. The surface roughness of these surface-roughened resinfilms laminated to the sheets coated with a surface-roughened resin filmwas measured in the same manner as in Example 1. The results are shownin Table 6. TABLE 4 Resin composition Resin number Resin compositionPOL1 Polyethylene POL2 Polypropylene POL3 Ethylene-propylene copolymerPOL4 Polypropylene (90% by weight) + maleic anhydride-modifiedpolypropylene (10% by weight) POL5 Polyethylene (90% by weight) +acrylic acid-modified polyethylene (10% by weight) POL6 Polyethylene(90% by weight) + methyl acrylate-modified polyethylene (10% by weight)POL7 Polyethylene (90% by weight) + glycidyl methacrylate-modifiedpolyethylene (10% by weight) PEL1 Ethylene-propylene copolymer elastomer(MFR: 0.45 g/ 10 minutes) PEL2 Ethylene-propylene copolymer elastomer(MFR: 8 g/10 minutes) PEL3 Ethylene-propylene copolymer elastomer (MFR:25 g/ 10 minutes) PEL4 Ethylene-propylene copolymer elastomer (MFR: 30g/ 10 minutes)

TABLE 5 Surface-roughened resin film Lower layer film Upper layer filmOlefin component Physical property of film [polyester + ContentThickness Surface Sample incompatible resin] PES resin (% by(upper/lower: roughness number (sample number) Type Type weight) μm)(Ra: μm) Category 17 PES2 + PP PES1 — — 10 + 15 0.08 Comparative (No.11) example 18 PES2 + PP PES1 POL4 1 10 + 15 0.22 Present (No. 11)invention 19 PES2 + PP PES1 POL4 5 10 + 15 0.21 Present (No. 11)invention 20 PES2 + PP PES1 POL4 10 10 + 15 0.20 Present (No. 11)invention 21 PES2 + PP PES1 POL4 15 10 + 15 0.22 Present (No. 11)invention 22 PES2 + PP PES1 POL4 30 10 + 15 0.21 Present (No. 11)invention 23 PES9 + PE PES6 POL3 15  3 + 47 0.74 Present (No. 13)invention 24 PES9 + PE PES6 POL5 15 15 + 10 0.73 Present (No. 13)invention 25 PES6 + EP PES9 POL6 15 15 + 10 0.46 Present (No. 14)invention 26 PES6 + EP PES9 POL7 15 20 + 10 0.47 Present (No. 14)invention 27 PES1 + PMC PES1 PEL1 15 15 + 10 0.34 Present (No. 15)invention 28 PES1 + PMC PES1 PEL2 15 25 + 10 0.35 Present (No. 15)invention 29 PES9 + PE PES6 PEL3 15 12 + 2  0.75 Present (No. 13)invention 30 PES6 + EP PES1 + PEL4 15 10 + 25 0.46 Present (No. 14) PES6invention 31 PES1 + PMC PES6 POL3 + PEL3 10 + 5 15 + 10 0.21 Present(No. 15) invention[Surface-Treated Steel Sheet]

-   1) Electrolytic chromate-treated steel sheet (represented by TFS in    Table 6 and in the following)-   Sheet thickness: 0.18 mm-   Amount of metal chromium: 160 mg/m²-   Amount of hydrated chromium oxide: (in terms of chromium) 19 mg/m²-   Heating temperature: 240 to 280° C.-   2) Tin plate (represented by ET in Table 6 and in the following)-   Sheet thickness: 0.18 mm-   Amount of tin coating: 200 mg/m²-   Amount of hydrated chromium oxide: (in terms of chromium) 9 mg/m²-   Heating temperature: 200° C.-   3) Aluminum alloy (JIS 5052H39) (represented by AL in Table 6 and in    the following)-   Sheet thickness: 0.26 mm-   Coating amount: (in terms of phosphorus) 11 mg/m² (in terms of    chromium) 7 mg/m²-   Heating temperature: 240 to 280° C.

Example 4 Sample Numbers 44 to 46

A two-layer polyester resin film consisting of an upper layer ofpolyethylene terephthalate (with a thickness of 20 μm, represented byPET in Table 6) and a lower layer of polyester resin (ethyleneterephthalate (88 mol %)-ethylene isophthalate (12 mol %) copolymer,with a thickness of 5 μm, represented by ET (88)-EI(12) in Table 6) andthe white polyester resin film shown in Example 3 were laminated to thesame respective sides of TFS as shown in Example 3 by using thepress-bonding rolls in the same manner as Example 3. Then, the laminatedsteel sheet was heated to 230 to 240° C., and by using a pair of embossrolls consisting of an emboss roll whose surface had been roughened soas to have a surface roughness Ra (JIS B 0601) of 0.7 μm as one roll andan elastic roll lined with silicone rubber as the other roll, thepattern of the roughened surface of the emboss roll was transferred tothe surface of the resin film by holding and pressing the laminatedsteel sheet by applying a pressure load of 20000 to 120000 N, whereby ametal sheet coated with a surface-roughened resin film was produced. Thesurface roughness of these surface-roughened resin films laminated tothe sheets coated with a surface-roughened resin film was measured inthe same manner as in Example 1. The results are shown in Table 6. TABLE6 Structure of metal sheet coated with a surface-roughened resin filmSurface roughness Resin film Presence or of film after Sample MetalInner surface of can Outer surface absence of lamination number sheetUpper layer Lower layer of can adhesive (Ra: μm) Category 32 ET PES2 +T1 — White ET Presence 0.24 Present (88)-EI (12) invention 33 TFS PES6 +S1 — White ET Absence 0.15 Comparative (88)-EI (12) example 34 ET PES8 +S3 — White ET Presence 0.68 Present (88)-EI (12) invention 35 ET PES2 +PP — White ET Presence 0.20 Present (88)-EI (12) invention 36 TFS PES6 +EP — White ET Absence 0.46 Present (88)-EI (12) invention 37 ET PES1 +PMC — White ET Presence 0.46 Present (88)-EI (12) invention 38 AL PES2 +PP PES1 + POL4 White ET Presence 0.22 Present (88)-EI (12) invention 39AL PES2 + PP PES1 + POL4 White ET Presence 0.20 Present (88)-EI (12)invention 40 AL PES2 + PP PES1 + POL4 White ET Presence 0.21 Present(88)-EI (12) invention 41 ET PES9 + PE PES6 + POL5 White ET Presence0.73 Present (88)-EI (12) invention 42 TFS PES6 + EP PES9 + POL7 WhiteET Absence 0.46 Present (88)-EI (12) invention 43 ET PES1 + PMC PES6 +POL3 + PEL3 White ET Presence 0.21 Present (88)-EI (12) invention 44 TFSPET ET (88)-EI (12) White ET Absence 0.18 Comparative (88)-EI (12)example 45 TFS PET ET (88)-EI (12) White ET Absence 0.34 Present (88)-EI(12) invention 46 TES PET ET (88)-EI (12) White ET Absence 0.63 Present(88)-EI (12) invention 47 ET PET-BO — White ET Presence 0.13 Comparative(88)-EI (12) example 48 ET PET-B0 — White ET Presence 0.28 Present(88)-EI (12) invention 49 ET PET-B0 — White ET Presence 0.59 Present(88)-EI (12) invention

Example 5 Sample Numbers 47 to 49

A biaxially stretched film of polyethylene terephthalate (with athickness of 25 μm, with an intrinsic viscosity of 0.8, represented byPET-BO in Table 6) was heated to 160° C., and by using a pair of embossrolls consisting of an emboss roll whose surface had been roughened soas to have a surface roughness Ra of 0.7 μm as one roll and an elasticroll lined with silicone rubber as the other roll, the pattern of theroughened surface of the emboss roll was transferred to the surface ofthe resin film by holding and pressing it by applying a pressure load of20000 to 120000 N, whereby a surface-roughened resin film was produced.An epoxy-based resin was applied to the unroughened surface of thissurface-roughened resin film and one side of the white polyester resinfilm as shown in Example 3, and the solvent was removed by drying. Theseresin films were placed so that the surfaces, to which the adhesive wasapplied, was brought into contact with the ET surface, and they werelaminated to the same respective surfaces of ET as shown in Example 3 byusing the press-bonding rolls in the same manner as in Example 3,whereby a metal sheet coated with a surface-roughened resin film wasproduced. The surface roughness Ra of these surface-roughened resinfilms laminated to the sheets coated with a surface-roughened resin filmwas measured in the same manner as in Example 1. The results are shownin Table 6.

Example 6 Welded Can

A rectangular blank was cut out from the metal sheets coated with asurface-roughened resin film of the sample numbers 34, 35, 47 and 49 androlled up so that the surface coated with the white resin film becamethe outer surface of the can, and the edges were superimposed andseam-welded, whereby a welded can barrel was produced. The resin film onthe edges to become a welded part had been removed by cutting inadvance. Then, after it was corrected by sticking a correction tape madeof a polyester resin film on the welded part, a bottom plate was seamed,whereby a welded can was produced. Tuna in oil packed in a commerciallyavailable can for business use was ground with a mixer and packed inthis welded can and the top plate was seamed. Then, heat sterilizationwas carried out in steam at 130° C. for 90 minutes. Then, after the topplate was opened and the contents were taken out by placing the canupside down, the degree of the remaining contents adhering to the insidewall of the can was visually observed and the easiness of taking out thecontents was evaluated in accordance with the following criteria.

<Evaluation of Easiness of Taking Out Contents>

Contents adhering to the inside wall of the can are hardly observed.

Contents adhering to the inside wall of the can are slightly observed,however they can be almost removed by shaking the can by hand.

ρ: Contents adhering to the inside wall of the can are observed, and alarge portion of them remains after shaking the can by hand.

Contents adhering to the inside wall of the can are observed, and theyare hardly removed by shaking the can by hand. The results of theevaluation are shown in Table 7.

Example 7 Drawn Can

A circular plate blank was punched out from the metal sheets coated witha surface-roughened resin film of the sample numbers 37, 39, 42, 44 and46 and formed into a drawn can at a drawing ratio of 1.88 so that thesurface coated with the white resin film became the outer surface of thecan. In addition, a metal sheet coated with a resin film (sample number50), which had the same structure as the sample number 42 except forusing a polyester resin (PES6) which did not contain ethylene-propylenecopolymer in the upper layer film of the two-layer resin film coatingthe surface opposite to the surface coated with the white resin film,was produced. A circular plate blank was cut out from this metal sheetcoated with a resin film in the same manner as above and a drawn can wasformed in the same manner as above, except for using a punch, whosesurface had been rough-finished by a grinding process so as to have asurface roughness Ra of 0.78 μm. Then, the surface roughness of theresin film on the inside wall of the drawn can was measured in the samemanner as in Example 1. The results of the measurement are shown inTable 7. It is found that the surface roughness of the resin filmincreases by undergoing a drawing process. Then, the same contents as inExample 6 were packed in the drawn can and the top plate was seamed.Then, after heat sterilization was carried out in the same manner as inExample 6, the top plate was opened, and the easiness of taking out thecontents was evaluated in the same manner as in Example 6. The resultsof the evaluation are shown in Table 7.

Example 8 Drawn and Ironed Can

A circular plate blank was punched out from the metal sheets coated witha surface-roughened resin film of the sample numbers 33, 36, 43, 45 and48 and formed into a cup by a two-step drawing process (the totaldrawing ratio of 2.21) so that the surface coated with the white resinfilm became the outer surface of the can. Then this cup was formed intoa drawn and ironed can (represented by DI can in Table 7) by a two-stepironing process (the total ironing ratio of 50%). In addition, a metalsheet coated with a resin film (sample number 51), which had the samestructure as the sample number 36 except for using a polyester resin(PES6) which did not contain ethylene-propylene copolymer in the resinfilm coating the surface opposite to the surface coated with the whiteresin film, was produced. A circular plate blank was punched out fromthis metal sheet coated with a resin film in the same manner as above,and after a drawn cup was formed in the same manner as above, a drawnand ironed can was formed in the same manner as above except for using apunch, whose surface had been rough-finished by a grinding process inthe ironing step so as to have the surface roughness Ra of 0.55 μm.Then, the surface roughness of the resin film on the inside wall of thedrawn and ironed can was measured in the same manner as in Example 1.The results of the measurement are shown in Table 7. It is found thatthe surface roughness of the resin film increases by undergoing adrawing and ironing process. Then, the same contents as in example 6were packed in the drawn and ironed can and the top plate was seamed.Then, after heat sterilization was carried out in the same manner as inExample 6, the top plate was opened, and the easiness of taking out thecontents was evaluated in the same manner as in Example 6. The resultsof the evaluation are shown in Table 7. TABLE 7 Evaluation resultsSurface rough- Metal ness of resin Easi- sheet film (Ra: μm) ness ofType coated Before After taking of with proc- pro- out can resin filmcessing cessing contents Category Welded No. 34 0.68 —

Present invention can No. 35 0.20 —

Comparative example No. 47 0.13 —

Comparative example No. 49 0.59 —

Present invention Drawn No. 37 0.46 0.74

Present invention can No. 39 0.20 0.50

Present invention No. 42 0.46 0.77

Present invention No. 44 0.18 0.41 ρ Comparative example No. 46 0.630.95

Present invention No. 50 — 0.57

Present invention DI can No. 33 0.15 0.39 ρ Comparative example No. 360.46 0.72

Present invention No. 43 0.21 0.53

Present invention No. 45 0.34 0.67

Present invention No. 48 0.28 0.61

Present invention No. 51 — 0.59

Present inventionNote)—: Measurement was not performed.

As shown in Table 7, in the case where the metal sheet coated with asurface-roughened resin film of the present invention is formed into awelded can, the contents packed in the welded can can be easy to takeout. In addition, in the case where the metal sheet coated with asurface-roughened resin film of the present invention is formed into adrawn can or a drawn and ironed can, the contents packed in such a cancan be also easy to take out. Further, in the case where the metal sheetcoated with a resin film is formed into a drawn can or a drawn andironed can by using a punch whose surface has been roughened, thecontents packed in such a can can be also easy to take out.

INDUSTRIAL APPLICABILITY

The surface-roughened resin film of the present invention is asurface-roughened resin film whose surface has been roughened byincorporating an inorganic particle in a polyester resin or byincorporating a resin incompatible with a polyester resin such as apolyolefin resin in a resin.

In addition, the metal sheet coated with a surface-roughened resin filmof the present invention can be obtained by laminating, to a metalsheet, such a surface-roughened resin film or a surface-roughened resinfilm obtained by embossing the surface of the resin film. Alternatively,it can be obtained by embossing a metal sheet coated with a resin filmobtained by laminating a resin film whose surface has not been roughenedto a metal sheet.

Such a metal sheet coated with a surface-roughened resin film is formedinto a welded can, a drawn can or a drawn and ironed can, therebyobtaining the metal can having a surface coated with a surface-roughenedresin film of the present invention. The surface roughness of the resinfilm is further increased by undergoing a drawing process or a drawingand ironing process. The metal can having a surface coated with asurface-roughened resin film of the present invention can be alsoobtained by processing a metal sheet coated with a resin film obtainedby laminating a resin film whose surface has not been roughened to ametal sheet by drawing or drawing with ironing with the use of a punchwhose surface has been roughened.

In the case of taking out the contents packed in such a metal can of thepresent invention having a surface coated with a surface-roughened resinfilm, since the surface of the resin film has been roughened, thecontents do not firmly adhere to the can wall, whereby it can be easy totake out.

1. A surface-roughened resin film comprising a polyester resin filmwhose surface roughness Ra (JIS B 0601) is 0.2 μm or greater.
 2. Thesurface-roughened resin film according to claim 1 comprising a polyesterresin film whose surface roughness Ra (JIS B 0601) is 0.5 μm or greater.3. The surface-roughened resin film according to claim 1, formed byextruding a polyester resin obtained by incorporating therein 1% or moreby weight of an inorganic particle with a particle size of 1 μm orgreater.
 4. The surface-roughened resin film according to claim 3,wherein the inorganic particle is one or more kinds of titanium dioxide,zinc oxide, calcium carbonate and silicone dioxide.
 5. Thesurface-roughened resin film according to claim 1, formed by extruding aresin obtained by incorporating in the polyester resin film 5 to 30% byweight of a resin incompatible with the polyester resin film.
 6. Thesurface-roughened resin film according to claim 5, wherein the resinincompatible with the polyester resin film is one or more kinds of apolyolefin resin and polymethylmethacrylate.
 7. A surface-roughenedresin film comprising a two-layer film consisting of a surface-roughenedresin film according to claim 1 as the upper layer film and a lowerlayer film which has been provided thereunder and is composed of a resinobtained by blending one or more kinds of polyester resins and apolyolefin component composed of at least one kind selected from thegroup consisting of a polyolefin resin and polyolefin elastomer.
 8. Thesurface-roughened resin film according to claim 7, wherein a polyolefinresin or a resin composed of a polyolefin resin and polyolefin elastomeris used as the polyolefin component.
 9. The surface-roughened resin filmaccording to claim 6, wherein the polyolefin resin is a resin composedof one or more kinds of polymer resins of 1-alkene having 2 to 8 carbonatoms.
 10. The surface-roughened resin film according to claim 9,wherein the 1-alkene polymer resin is any of polyethylene,polypropylene, ethylene-propylene copolymer.
 11. The surface-roughenedresin film according to claim 6, wherein the polyolefin resin is apolyolefin resin obtained by polymerization with a metallocene catalyst.12. The surface-roughened resin film according to claim 7, wherein atleast a part of the polyolefin resin is a modified polyolefin resinobtained by modification with any of maleic anhydride, acrylic acid,acrylic ester and diglycidyl methacrylate.
 13. The surface-roughenedresin film according to claim 7, wherein the polyolefin elastomer isethylene-propylene copolymer elastomer produced in plant with a meltflow rate (MFR: 230° C.) of 0.4 to 30 g/10 minutes.
 14. Thesurface-roughened resin film according to claim 7, wherein the blendedresin constituting the lower layer film contains 1 to 30% by weight ofthe polyolefin component.
 15. A metal sheet coated with asurface-roughened resin film, formed by laminating a surface-roughenedresin film according to claim 1 to a metal sheet.
 16. A metal sheetcoated with a surface-roughened resin film, formed by being coated witha polyester resin film having an uneven pattern formed on the surface byan embossing process.
 17. The metal sheet coated with asurface-roughened resin film according to claim 16, wherein the surfaceroughness Ra (JIS B 0601) of the surface-roughened resin film is 0.2 μmor greater.
 18. The metal sheet coated with a surface-roughened resinfilm according to claim 17, wherein the surface roughness Ra (JIS B0601) of the surface-roughened resin film is 0.5 μm or greater.
 19. Aprocess for producing a metal sheet coated with a surface-roughenedresin film characterized by laminating a surface-roughened resin filmaccording to claim 1 to a metal sheet.
 20. A process for producing ametal sheet coated with a surface-roughened resin film characterized bylaminating a polyester resin film having an uneven pattern formed on thesurface by an embossing process to a metal sheet.
 21. A process forproducing a metal sheet coated with a surface-roughened resin filmcharacterized by laminating a polyester resin film to a metal sheet andthen embossing the surface of the polyester resin film.
 22. A metal canhaving a surface coated with a surface-roughened resin film, formed byprocessing a metal sheet coated with a resin film, wherein the surfaceroughness Ra (JIS B 0601) of the resin film after being formed into acan is 0.5 μm or greater.
 23. The metal can having a surface coated witha surface-roughened resin film according to claim 22, wherein the resinfilm is a polyester resin film.
 24. A metal can having a surface coatedwith a surface-roughened resin film, formed by processing a metal sheetcoated with a surface-roughened resin film according to claim 15,wherein the surface roughness Ra (JIS B 0601) of the resin film afterbeing formed into a can is 0.5 μm or greater.
 25. The metal can having asurface coated with a surface-roughened resin film according to claim22, formed by processing a metal sheet coated with a resin film bydrawing or by drawing with ironing with the use of a punch whose surfacehas been roughened.
 26. A process for producing a metal can having asurface coated with a surface-roughened resin film characterized byprocessing a metal sheet coated with a polyester resin film and formingit into a can body by drawing or by drawing with ironing with the use ofa punch whose surface has been roughened.